What types of insulation are the most cost effective for my detached house? Cavity / roof / replacing windows doors etc..
Dependant on where and what needs insulating, if it's a roof loft , generally use 300 mm insulation, there are more space age ways to insulate you insulating the inside of the roof thereby giving more space on the floor to utilise ..
nowadays insulated plasterboards external and internal are very effective, love insulation and cavity is free with gov grants,
roof / replacing windows doors etc..
All of these is what you really want but order of me doing these to my own property would be